1. Field of the Invention
The invention relates to switches. More particularly, the invention relates to an electrical switch made of silicon.
2. Description of Prior Art
Pen technology is a technology whereby a pen stylus is designed to send signals to a computer such that a digitized drawing tool for the computer is provided. A digitized drawing pen can be used for example by a professional graphic artist, by a business analyst as a presentation tool, and by a young student at home for a school project. An example of a prior art is a digitizer, which is a combination of a digital pen and a tablet. For example. M. Pladula. H. Matthews. Digitizer Stylus With Pressure Tranducer, U.S. Pat. No. 4,786,764 (Nov. 22, 1988) discloses a stylus pressure switch that is automatically activated when a tip of the stylus is pressed against a digitizer tablet with sufficient force.
Padula and Matthews discuss how data from a stylus and tablet combination in one embodiment provide input to electronic circuits, which then convert the signals into the coordinate position of the stylus on the tablet. Padula and Matthews also discuss how in another embodiment the conversion is into other signals, which in conjunction with a microprocessor are used to drive a display.
In both embodiments it is desirable that the stylus and tablet system be operative only when the stylus is intentionally pressed against the digitizer tablet surface. To obtain this level of control of the operation of the stylus and the tablet, switching elements are generally included within the stylus housing. Switching, elements can isolate the stylus from data processing circuits to eliminate spurious data inputs or can connect the stylus as required in operation. Padula and Matthews disclose a pressure switch that comprises a transducer in the form of an ink layer having electrical resistance that varies as a function of the pressure applied to the layer. Electrodes contact the ink layer transducer, providing a circuit including a variable resistance. Each electrode is formed as a layer of conductive ink. It would be advantageous to provide a switch element that is of simple design efficient, of durable material, user-friendly and economical to assemble.
Membrane switches can be simple switches. Membrane switches, according to D. Gross, Membrane Switch with Pivotable Rocker, U.S. Pat. No. 4,618,754 (Oct. 21, 1986) have been widely used for many low-voltage applications. Gross attributes the wide use in large part to the switch's simple mechanical construction and its flat front face, which allows convenient placement of descriptive graphics and which seals the switch interior from contamination. Membrane switches generally may comprise a circuit board having spaced electrical contacts fixed on its upper surface, an overlaying spacer with an aperture aligned with each contact, and a flexible membrane overlaying the spacer. An electrical contact on the underside of the membrane is normally spaced a predetermined distance above the circuit board contacts, whereby a normally open switch is provided. A downward force applied to the membrane lowers the membrane contact into electrical contact with the spaced circuit board contacts to short the latter together and thereby close the normally open switch.
The Gross Patent document discloses a membrane switch that includes a normally open set of electrical contacts and a normally closed set of electrical contacts. In one embodiment a downward force applied to the switch pivots an elongated flat rocker to close the normally open contacts and simultaneously open the normally closed contacts. When the force is removed the pivoting of the rocker is yieldably resisted by an overlaying resilient membrane that forcibly returns the rocker to its original position. In another embodiment a downward force applied to the switch lowers the center of a special disk into contact with an underlying circuit board to close the normally open contacts. The force simultaneously deforms the disk's periphery upwardly to open the normally closed contacts. When the force is removed internal stress in the deformed disk returns the disk to its original position.
Membrane switches are used in keyboard design. See for example W. Larson, Membrane Switch Apparatus Having Sequential Bridging Contact Arrangement, U.S. Pat. No. 3,987,259 (Oct. 19, 1976), W. Larson. Keyboard Membrane Switch Having Threshold Force Structure, U.S. Pat. No. 4,017,697 (Apr. 12, 1977), L. Latasiewicz, Membrane Switch Assembly With Improved Spacer, U.S. Pat. No. 4,345,119 (Aug. 17. 1982), P. Rutten, Membrane Switch, U.S. Pat. No. 5,561,278 (Oct. 1, 1996), and M. Kaizu, (Click-action membrane switch, European Patent Application No. 0 531 973 A2 (Sep. 9, 1992). In keyboard technology, the applied force to activate a switch is typically a downward force of a probe such as a finger. The force to activate a switch in a stylus housing can be an upward force reactive to the downward force of a stylus in operation.
It would be advantageous to provide a switch element that comprises the following, properties. The switch has a simple and flexible design and is economical to assemble. It is efficient, made of durable material, user-friendly and has a shape that incorporates the upward reactive force of a stylus in operation.